Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
491 FXUS66 KSEW 301011 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 311 AM PDT Tue Apr 30 2024 .SYNOPSIS...Shower activity will continue through the evening tonight before shifting southward. Conditions will be drier and warmer Wednesday through Friday, with cooler and wetter weather returning by the weekend. && .SHORT TERM /TODAY THROUGH THURSDAY/...A surface low will continue to push onshore through the morning and slide eastward throughout the day as an upper trough axis shifts over the Pacific Northwest. Scattered showers will continue to stream eastward through the morning hours, slowly shifting southward through the afternoon as high pressure builds inland behind. The core of the surface low will track onshore along the Columbia Gorge today, enhancing instability with ensembles showing an average of 200-300 J/kg this afternoon mainly south and west of Seattle. Lightning and graupel cannot be ruled out of any stronger showers that develop in the afternoon. Precipitation will taper off by the evening, with temperatures staying on the cool side peaking in the mid 50s across the lowlands. Weak ridging will allow conditions to dry out late Tuesday, and decreasing cloud cover overnight into Wednesday morning will allow some locations to see temperatures bottom out near freezing. Otherwise, dry conditions will prevail for much of the day Wednesday with highs warming up to the upper 50s and lower 60s. Another weak low pressure system will pass over the region late Wednesday into Thursday, with some uncertainty remaining over the exact track of the storm system. While most models bring this system south of the area, a chance of precipitation is maintained for much of the area through Thursday, favoring higher terrain. Snow levels will hover near 3500-4000 ft with light precipitation amounts, and temperatures will continue a warming trend increasing into the low to mid 60s. .LONG TERM /FRIDAY THROUGH MONDAY/...Weak ridging will expand inland late Tuesday through Friday morning, with the potential for some areas to approach 70 degrees by Friday afternoon. A low pressure system is on track to move towards the Pacific Northwest by next weekend, but forecast models show fairly large differences in terms of placement and timing of any precipitation with this system. While uncertainty remains through the weekend, ensembles favor a cooler and wetter troughing pattern through Monday with a return to near-normal or slightly cooler temperatures. Lindeman && .AVIATION...Westerly flow aloft will become more northerly as an upper level low moves inland today. At the surface, a weak low offshore will gradually make its way inland towards the WA/OR border late this morning into early this afternoon. Radar shows scattered shower activity across the area this morning, with the heaviest showers currently moving inland along the coast. Current conditions are a mix of VFR and MVFR across the area terminals this morning, but expect conditions to become more widespread MVFR through the early morning hours. MVFR ceilings then look to lift back to widespread VFR by this afternoon. Isolated thunderstorms will be possible at times for terminals mainly along the coast and from the central Sound southward, though confidence is too low at this time to include in TAFs. Showers will gradually taper across the region this afternoon and evening. Low level winds persist primarily out of the south at 3-7 kt this morning, but look to shift to the north late morning and increase to 5-10 kt at times. Winds then look to ease back to 3-7 kt by this evening. KSEA...Current conditions VFR with southerly winds persisting generally at 3-7 kt. Expect conditions to become MVFR this morning and to persist through 18Z, before lifting back to VFR this afternoon. Additional shower activity is likely at the terminal today. Isolated thunder cannot be ruled out, though confidence is low at this time. Winds look to shift to the north between 18-20Z and persist at 5-10 kt through the evening hours before easing back to 3-7 kt between 03-06Z Weds. 14 && .MARINE...A few small craft gusts continue across portions of the Eastern Strait early this morning, but expect the wind to ease over the next few hours. A weak surface low will traverse the coastal waters today and push inland along the WA/OR border by late morning/early afternoon. Seas look to briefly build towards 10 feet over the outer coastal waters this morning, so have issued a small craft for these zones through this afternoon. May see another low-end advisory strength push of westerly winds through the Strait tonight into early Wednesday, with probabilities highlighting a 50-60 percent chance of gusts occasionally exceeding 21 kt. Have held off of small craft issuance for now, however this will continue to be monitored through the day. High pressure will then build back into the area waters tonight into Wednesday, before yet another low and its associated frontal system move into the region Wednesday night into Thursday. The period will remain active, with another frontal system expected to traverse the area waters Friday night into the weekend. Seas over the outer coastal waters look to subside below 10 ft tonight. Seas over all the coastal waters will continue to subside into midweek, hovering between 3 to 6 ft Wednesday through Friday. Seas will then increase closer to 6 to 8 ft again over the weekend. 14 && .HYDROLOGY...No river flooding is expected over the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory until 5 PM PDT this afternoon for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm. && $$